Process for the purification of phosphoric acid containing arsenic



Patented Nov. 24, 1925.

OFFICE.

OTTO WOLFES AND HORST MAEDER, OF DARMSTADT, GERMANY.

. PROCESS FOR THE PURIFIOIKTION OF PHOSPHORIC ACID CONTAINING I No Drawing.

To aZZ whom it may concern Be it known that we, Or'ro VVoLFEs, residing at Darmstadt,'49 Hoftmannstrasse, Germany, and HORST MAnnEn, residing at Darmstadt, 31 Wittmannstrasse, Germany, both citizens of the Republic of Germany, have invented a Processfor the Purification of Phosphoric Acid Containing Arsenic, of which the following is a clear, full, and

exact'description.

Hitherto phosphoric acid was purified from arsenic either bytreating ordinary commercial phosphoric acid with sulphureted hydrogen or heating it to a temperature of more than 200 C. The former method sufi'ers from the disadvantage that the phosphoric acid is very apt to be contaminated by the oxidation products of the sulphureted hydrogen, while in the latter the arsenic is precipitated in such a very fine state of division that great difficulty is experienced in separating it from the acid. In addition, in consequence of the heating, c0ncentration of the phosphoric acid takes place,

a fact which renders operations more difficult.

Now, a very important madenamely, that phosphoric acid may be freed from arsenic by treating the acid with phosphoretcd hydrogen, whereupon the discovery was ARSENIC.

Application filed May 5, 1925. Serial No. 28,217. W

arsenic is precipitated in flakes which may be readily separated by filtration. centrifuging, or other similar means. The effect is that no contamination of the phosphoric acid by the purifying agent through oxidation can take place.

' Example.

. Into an earthenware vessel provided with several inlet and outlet openings which can 51 be closed as required'place about 100 litres of phosphoric acid 80 per cent, replace the air by C0 and pass phosphorcted hydrogen through theqiquid whereupon arsenic will be thrown down in the form of'brownish-black flakes. After the reaction is com- DR. OTTO WOLFES. v DR. HORST MAEDER. 

